Mac: add new header file needed for replacing system() calls with posix_spawn() calls.

lib/mac/mac_spawn.h

@@ -0,0 +1,26 @@
+// This file is part of BOINC.
+// http://boinc.berkeley.edu
+// Copyright (C) 2017 University of California
+//
+// BOINC is free software; you can redistribute it and/or modify it
+// under the terms of the GNU Lesser General Public License
+// as published by the Free Software Foundation,
+// either version 3 of the License, or (at your option) any later version.
+//
+// BOINC is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+// See the GNU Lesser General Public License for more details.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with BOINC.  If not, see <http://www.gnu.org/licenses/>.
+
+// system() is deprecated in Mac OS 10.10.
+// Apple says to call posix_spawn instead.
+
+#ifndef _MAC_SPAWN_H_
+#define _MAC_SPAWN_H_
+
+int callPosixSpawn(const char *cmdline);
+
+#endif  // _MAC_SPAWN_H_